1. Technical Field
The present invention relates generally to circuit design software, and more particularly, to a methodology and computer program that perform design checks and design modification of buried blind via structures to minimize vertical current discontinuities.
2. Description of the Related Art
High-density interconnect schemes within and between processor packages and other very-large-scale integrated (VLSI) circuits, typically use a large number of circuit layers to connect one or more dies to electrical terminals disposed on one or more surfaces of the package, as well as to interconnect multiple dies in multi-die packages. With the high frequencies and/or narrow pulse widths of critical signals in present-day VLSI circuits, special layout techniques are typically required for routing critical signal paths to minimize reflections, impedance mismatches and coupling between signal paths, according to electromagnetic analysis techniques. Signal reference planes such as power planes are also typically provided between signal layers to provide controlled signal path impedance and to shield overlapping signal paths from each other.
Blind vias are conductive structures that interconnect endpoints of conductive signal paths that extend on two layers of a multi-layer circuit, but that do not extend vertically beyond the endpoints. When a critical signal is passed through a blind via, a vertical current component is introduced that couples to nearby vias to form a return path loop. The greater the distance between a critical signal blind via and a low impedance return path, the larger the circuit inductance due to discontinuity introduced by the via. Further, if the net lowest impedance return path includes signal vias, undesired coupling to the signal vias will also occur.
Extensive electromagnetic circuit analysis is not typically undertaken for determining such inductive effects and coupling, as accurate models are complex and computation-intensive. Furthermore, such modeling would have to be performed for each design iteration, dramatically increasing design time. Existing non-analytic techniques, such as automated or visual inspection of signal paths are typically two-dimensional and therefore do not take into account the three-dimensional nature of the problem.
It is therefore desirable to provide a design methodology and computer program that minimize blind via vertical current discontinuities without requiring an extensive electromagnetic analysis and that take into account the three-dimensional nature of the current discontinuities.